The present invention relates to apparatus for ejecting material from a liquid. More particularly, the method and apparatus employed may be generally of the type described in WO-A-93-11866, WO-A-94-18011 and WO-A-95-32864, the disclosure of which is incorporated herein by reference. In the methods described in these patent applications an agglomeration or concentration of particles is achieved at an ejection location and from the ejection location particles are then ejected onto a substrate, e.g. for printing purposes. In the case of an array printer, plural cells each containing an ejection location may be arranged in one or more rows.
The present invention is directed towards novel constructions of such apparatus to improve operation and enhance operability, some of which were also disclosed, for the first time on the priority date of the present application, in FIGS. 4 to 6 of WO-A-97-27058, the disclosure of which is also incorporated herein by reference. Reference is also made to our WO-A-97-27056, WO-A-97-27057, and WO-A-97-27060.
EP-A-0703081, EP-A-0046295 and U.S. Pat. No. 4396925 disclose ejection apparatuses which include projecting electrodes which act to cause ejection of liquid from the apparatus.
According to a first aspect of the present invention there is provided an ejection apparatus for ejecting material from a fluid, the apparatus comprising an ejection cell for containing fluid from which the material is to be ejected, the cell having a single ejection upstand formed of a dielectric material and extending outwardly of the cell and defining a location from which the material is ejected, and one or more ejection electrodes disposed in the cell substantially surrounding the ejection upstand.
The term xe2x80x98substantially surroundingxe2x80x99 is preferably used in the context of this application, to mean that the ejection electrode or electrodes extend around at least 50% of the periphery of the ejection upstand, but, preferably, the ejection electrodes extend around a greater part of the periphery in order to surround the ejection upstand to the greatest extent possible.
Preferably, the ejection electrode, which may be single or multi-part, extends substantially completely around the ejection upstand.
According to a second aspect of the invention there is provided an ejection apparatus for ejecting material from a fluid, the apparatus comprising an ejection cell for containing fluid from which the material is to be ejected, the cell having an ejection upstand formed of a dielectric material and extending outwardly of the cell and defining a location from which the material is ejected, and a pair of ejection electrodes, one disposed on each side of the ejection upstand. The ejection electrodes are electrically connected so as to provide the same voltages in use.
The ejection upstand, which in use pins a fluid meniscus at the outer extremity of the cell, may take one of a number of different forms, for example comprising a corner of a separator which at least partially divides the cell into two halves, one on each side of the separator. In such case, the separator may be substantially planar (or plate-like) and plural cells may be arranged in closely spaced alignment, each cell being separated from its neighbors by a pair of second plate-like separators, one on each side. Each second separator is thus common to the adjacent cells and alternate separators are used to form the ejection upstands. Preferably, the second separators do not project outwardly of the cells, but rather define the outer boundaries of the cells, through which the ejection upstands project. The xe2x80x98stackxe2x80x99 of plate-like separators thus define a row of ejection cells having ejection upstands at one corner and the side edges of the cells may be closed by cover plates suitably positioned.
The ejection electrodes may comprise multi-part electrodes, a first part being disposed on a face of the ejection upstand and a second part on the opposing face of the adjacent separator.
The cover plates may themselves constitute additional or secondary electrodes to enhance the electric field around the ejection upstands.
Providing the cells with separators and electrodes as described above provides shielding for the ejection location from the voltages applied to the electrodes of adjacent cells and fluidic isolation for the ejection location when ejection voltages are applied to the electrodes of adjacent cells.